Present day motor vehicles include numerous complex mechanical and electrical systems. Computers are used on-board to monitor the performance of such systems and assist in the efficient operation of the motor vehicle. During preventative maintenance or repair, an external diagnostic system can be directly coupled to the on-board computer thereby allowing for an efficient method of identifying motor vehicle performance problems and verifying corrective measures are effective in resolving such problems.
An example of the use of a computer system to monitor motor vehicle performance is found in the diesel trucking industry. For example, some diesel trucks manufactured by Cummings, Inc., of Columbus, Ind., include an on-board computer system which communicates with system and subsystem components of the diesel truck by means of a serial communication bus structure, referred to as the J1708 bus (hereinafter the "J-bus"). The protocol for communication on the J-bus has been standardized by the Truck and Bus Data Format Subcommittee of the Truck and Bus Electrical and Electronics Committee and by the S.1 Electrical & Electronics Study Group of the Maintenance Council in "Joint SAE/TMC Electronic Data Interchange Between Microcomputer Systems in Heavy-Duty Vehicle Applications" issued January 1988 and revised March 1996. Electrical and mechanical systems on the diesel truck are fitted with transmitters which are in turn coupled to the J-bus. Each transmitter may dump data onto the bus or respond to requests for information generated by the on-board computer system. During truck maintenance activities, a ground station can be coupled to the on-board computer system to monitor motor vehicle performance parameters. However, this requires the motor vehicle or diesel truck to return to a maintenance station or other ground facility that includes the ground station hardware.
In the diesel truck industry, efficient motor vehicle (truck) performance is of paramount concern. Substantial costs are incurred when trucks are out of service due to system failure or when the trucks are operated at less than optimum performance levels. Accordingly, regular maintenance of each truck is required to minimize down time and running costs. However, the regular maintenance provided to the vehicles is itself quite costly. The trucks typically have to be brought into a central maintenance facility and directly coupled to diagnostic systems. In general the maintenance schedules are based on truck mileage, and do not take into account any other performance criteria for a given individual truck. No easy method of screening individual trucks based on performance data is available.